Embodiments of the invention relate generally to a system and method for biometric data capture, and more particularly to a contactless, high resolution handprint capture device.
It is well known that the patterns and geometry of fingerprints are different for each individual and are unchanged over time. Thus fingerprints serve as extremely accurate identifiers of an individual since they rely on un-modifiable physical attributes. The classification of fingerprints is usually based on certain characteristics such as arch, loop or whorl, with the most distinctive characteristics being the minutiae, the forks, or endings found in the ridges and the overall shape of the ridge flow. More recently, palm prints have also been identified as a potential enhanced means of biometric identification. It is recognized that palm prints can be used in combination with fingerprints to provide still a more foolproof “future modality” of biometrics.
Traditionally, fingerprints have been obtained by means of ink and paper, where a subject covers a surface of their finger with ink and presses/rolls their finger onto paper or a similar surface to produce a rolled fingerprint. More recently, various electronic fingerprint scanning systems have been developed that obtain images of fingerprints utilizing an optical fingerprint image capture technique. Such electronic fingerprint scanning systems have typically been in the form of contact based fingerprint readers that require a subject's finger to be put in contact with a screen and then physically rolled across the screen to provide an optically acquired full rolled-image fingerprint. However, such contact based fingerprint readers have significant drawbacks associated therewith. For example, in a field environment, dirt, grease or other debris may build up on the window of contact based fingerprint readers, so as to generate poor quality fingerprint images. Additionally, such contact based fingerprint readers provide a means of spreading disease or other contamination from one person to another.
In a most recent generation of electronic fingerprint scanning systems, contactless fingerprint readers have been proposed where fingerprints are captured without the need for physical contact with a subject's finger. However, existing contactless fingerprint scanning systems are limited regarding the type of fingerprint images they can acquire. For example, one existing type of contactless fingerprint scanning system is capable of acquiring a single flat image of the finger by utilizing a camera image. Such single flat images, however, do not provide the entire fingerprint data, as the use of one camera image does not allow for capture of a large area of the fingerprint.
Another existing type of contactless fingerprint scanning system acquires full 3D images of the fingers using a method such as structured light. Phase shifted structured light techniques use 3 or more images of the subject with a sine wave pattern projected onto the subject from some angle, with a shift of the pattern of a fraction of the pattern period between images. The projection angle and view angle must be different to create a triangulation effect which limits the ability to capture curved subjects such as fingers and palms. The result of such measurements is detailed 3D object measurement; however, these measurements require a high degree of stability during data capture necessitating careful fixturing of the finger to provide this stability. Additionally, the technique employed to create contrast between fingerprint ridges and valleys of a flat fingerprint image uses a shallow depth-of-field that prevents all areas of the finger, such as the top and sides of the finger, from being in clear focus in the same image.
Still another existing type of contactless fingerprint scanning system was recently described in U.S. patent application Ser. Nos. 12/694,840 and 12/889,663, filed by General Electric (GE) Company. The contactless fingerprint collection system described in the GE applications capture rolled equivalent fingerprint data using a fast switching optical system able to capture a set of images at multiple image depths. Each image has a high resolution focus which individually necessitates a shallow depth-of-field, just as a high-resolution microscope can only focus over a shallow depth at one time. The focus shift is created using a liquid crystal panel (LCP) in connection with a birefringent optical element built into a high-resolution lens system. The LCP is able to switch the polarization of the light in millisecond timescales, such that the polarization of the light rotates by 90 degrees, causing the light to see a different index of refraction in the birefringent optical element that then focuses the system to a different focal distance. Ortho-normal projection methods are employed after capture, such the images need not be perfectly registered.
However, there are certain restrictions on the contactless fingerprint collection system described in the GE applications. For example, the contactless fingerprint collection system is configured to only acquire fingerprint images and does not accommodate the collection of palm print images, with the fingerprint images thus only providing rolled equivalent fingerprint data without any such 2D equivalent palm print data. Additionally, a separate camera having a small field-of-view is employed for capturing each individual fingerprint, such that 3D shape information can only be gathered for fingers of the subject and not for the whole hand. Still further, the cameras employed are high resolution cameras having a native resolution of 1000 pixels-per-inch (PPI), thus necessitating use of a 30 mega-pixel or greater camera, adding to the expense of the system. Finally, contactless fingerprint collection system provides registration between multiple depth fingerprint images only in a software-based processing manner, such that the registration is computation/calculation intensive.
As set forth above, in future generations of biometric data capture devices, it may be desirable to capture palm prints as well as fingerprints to provide still a more foolproof modality of biometrics, i.e., capture a whole handprint. Such a handprint capture device would ideally provide for volumetric capture of the hand, with an extended depth of capture so as to enable capture of a plurality of hand shapes and poses and also enable 2D equivalent data of both the fingerprints (i.e., unrolled fingerprints) and the palm print. The handprint capture device would ideally use a lower resolution, lower cost camera that captures an image of the entire hand in one shot, with super-resolution processing being applied to increase resolution to a desired amount (e.g., 1000 PPI), to provide Level IV biometric data performance levels. The handprint capture device would also ideally provide registration between multiple depth handprint images by way of a guide mark-type registration device that lowers the computation/calculation demands of the system and speeds up the registration process.
It would therefore be desirable to design a system and method of acquiring a full contactless handprint image that excludes any contact between the hand and the handprint reader and that provides full rolled equivalent fingerprint data and 2D equivalent palm print data. It would further be desirable for such a system to employ a lower resolution, lower cost camera, with image processing that provides 1000 PPI or greater handprint image resolution.